Hydrocarbons, biocides, and sulfur

Abstract

From the Abstract: “This report describes studies of the hydrocarbons, biocides, sulfur, and related substances discharged from structures in the Buccaneer Gas and Oil Field, their distribution and fates in the surrounding environment, and an assessment of their ecological effects.

More than 120 substances have been identified in produced water discharges from the production platforms. These substances include n-alkanes, branched alkanes, cycloalkanes, olefins, aromatic hydrocarbons, alkylated aromatic hydrocarbons, biocides, and sulfur. Concentrations as high as 12 ppm of C12 to C38 alkanes, 170 ppb of methylnaphthalenes, 5 ppb of benzo[~]pyrene, and 1200 ppn of elemental sulfur were measured. Organic toxic pollutants (priority pollutants) detected in concentrations higher than 10 ppb were acenaphthylene, benzene, ethylbenzene, naphthalene, and toluene. Acrolein was employed as a biocide during the latter part of the study, but it was not detected in effluent samples. The discharge rate of produced water varies over a wide range, but it averaged about 1000 bbl (1.6 x 105 liters) per day toward the end of the study. Based on the meanconcentrations of constituents throughout the study, the annual discharge of alkanes and elemental sulfur was, respectively, 73 kg and 27 metric tons.

The major pool of contaminants in the region of the Buccaneer Field is in the surficial sediments. They contain concentrations as high as 50 ppn of "fresh" petroleum alkanes, and concentration gradients are clearly seen. While the concentration of elemental sulfur in the effluents is considerably higher than that of the alkanes, sulfur concentrations in the surficial sediments are comparable to those of the alkanes. This observation indicates that sulfur is dispersed and/or degraded in a manner different from that which is applicable to the alkanes.

Petroleum alkanes were usually detected at the air/sea interface in the mixing zone below the discharge pipes, but were found only occasionally in other seawater samples. Some seawater samples contained bacterial hydrocarbons which may have been produced by sulfur-bacteria supported by the discharged sulfur - a possible indirect source of alkanes attributable to oil and gas production activities.

Many different animal species were examined during this study. Petroleum hydrocarbons were encountered in some barnacles, fish, shrimp, and other organisms. A degree of correlation was found between the feeding habits of some fish and their content of petroleum hydrocarbons. Generally, those which fed on components of the platform fouling communitycontained higher concentrations of petroleum hydrocarbons than those which fed in the water column. Moreover, hydrocarbon concentrations were usually higher in the livers of these fish than in other tissues.

There was no evidence for biomagnification of hydrocarbons in the food web. Biogenic hydrocarbons usually predominated over petroleum hydrocarbons in biota samples. Acrolein was never detected in effluent samples, even though it was added to the produced water to suppress the populations of sulfur-bacteria. A scavenger is added by the platform operators to the effluent stream to remove excess acrolein prior to discharge. Elemental sulfur is the major component of the effluents, but it is of low toxicity and is dispersed and/or degraded more efficiently than the petroleum hydrocarbons. This substance is a nutrient for sulfur-bacteria and may contribute to the food web."